Fiber cement is typically made from a slurry of Portland cement (80-85%), which forms the matrix of the material, and a mixture of mineral, organic or synthetic fibers (15-20%), which contributes to making the cement material stronger and better at withstanding tensile and flexural strains. The slurry also generally contains different types of additives. Fibers used in fiber cement can include polypropylene, polyethylene, polyacrylic, cellulose, and/or asbestos. Fiber cement can be used in the manufacturing of a variety of parts, such as pipes and panels for example. Parts from fiber cement are known to be relatively inexpensive to manufacture while being very durable and capable of withstanding stress, due to the reinforcement provided by the fibers.
In the most popular fiber cement pipe manufacturing process, known as the Hatschek process, the slurry is dewatered using a rotary sieve cylinder and a very thin layer of fiber cement is produced. This thin layer is wrapped around a mandrel under pressure until a pipe with the desired wall thickness is obtained. After curing, the extremities of the pipe are cut to obtain the desired pipe length. The pipes are then finished in order to receive couplings that are produced by cutting larger diameter pipe into sections. This process requires the slurry to have a water-to-cement ratio of 200% w in order for the process to operate in a continuous mode. However, this process is typically only being used to manufacture cylindrical pipes.
Other existing methods for forming fiber cement parts include vibration molding, extrusion, and centrifugation molding. The water-to-cement ratio for such methods is generally below 50% w. When using a higher water-to-cement ratio, these methods produce fiber cement parts with a high porosity, compromising the mechanical properties of the part formed.
A continuous extrusion process known to the Applicant is disclosed in U.S. Pat. No. 6,398,998 by KRENCHEL et al. This process uses a flowable suspension containing cement, additives, other components such as fibers, and a surplus of water or other liquid. Between the inlet and the outlet of the molding section, a high pressure differential, produced by applying a high positive pressure to the slurry in the mold and by a pressure-regulating chamber located outside the mold, causes the liquid to be expelled through wall perforations distributed in a particular fashion in the draining section of the molding apparatus. This method leaves a dewatered shaped body with sufficient mechanical strength to be handled immediately upon completion of the process. This process requires continuous manufacturing and parts must be shaped with the same geometry restrictions as in a regular extrusion process.
A challenge for some of the above-mentioned processes resides in dewatering the slurry while preserving a uniform fiber distribution within the cement parts. Fibers must not be evacuated along with the water expelled from the slurry, and water needs to be evacuated rapidly from the slurry in order to increase productivity. In addition, the parts formed need to be sufficiently dewatered in order to have sufficient green strength, allowing for the part to be handled out of the mold and be cured. Another drawback of the processes discussed above is the limited geometry and/or size of the manufactured parts.
There is a need for a system and process which allow for the molding of fiber cement parts of various shapes and sizes. There is also a need for a system and a process for manufacturing such fiber cement parts quickly and reliably, and at a reasonable cost.